Hi. I am trying to use reCaptcha for a simple form and it's just not working out. I have successfully used it for another form and used that page as a template, but something has gone wrong. Please help.

<?php
/*
* This is a PHP library that handles calling reCAPTCHA.
* - Documentation and latest version
* http://recaptcha.net/plugins/php/
* - Get a reCAPTCHA API Key
* https://www.google.com/recaptcha/admin/create
* - Discussion group
* http://groups.google.com/group/recaptcha
*
* Copyright (c) 2007 reCAPTCHA -- http://recaptcha.net
* AUTHORS:
* Mike Crawford
* Ben Maurer
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/

/**
* Gets the challenge HTML (javascript and non-javascript version).
* This is called from the browser, and the resulting reCAPTCHA HTML widget
* is embedded within the HTML form it was called from.
* @param string $pubkey A public key for reCAPTCHA
* @param string $error The error given by reCAPTCHA (optional, default is null)
* @param boolean $use_ssl Should the request be made over ssl? (optional, default is false)